Drive-by-wire is a catch-all term that refers to a range of electronic systems that either supplement or replace traditional mechanical controls. Instead of using cables or hydraulic pressure to steer a vehicle, drive-by-wire technology uses electronic systems to activate the brakes, control driving and engine refueling.
There are three main drive components that electric drive systems typically replace with electronic controls: throttle, brakes, and steering. These systems are commonly referred to as:
- Electronic throttle control
Electronic throttle control
The most common form of control-by-wire technology, and the easiest to find in the wild, is electronic throttle control. Unlike traditional throttle controls, which connect the gas pedal and throttle with a mechanical cable, these systems use a range of electronic sensors and actuators.
Vehicles with computerized fuel control have used gas sensors for decades. These sensors tell the computer the position of the throttle, but the throttle itself is still activated by the physical cable. In vehicles that use true electronic throttle control (ETC), there is no physical connection between the gas pedal and the throttle. Instead, the accelerator sends a signal that causes the electromechanical actuator to open the throttle.
This is often considered the most secure type of wired technology because it is extremely easy to implement this type of system with a robust, fault-tolerant design. Just as the throttle will simply close if the mechanical throttle cable brakes, electronic throttle control systems can be designed to close the throttle if it is no longer receiving input from the pedal sensor.
Some consider wire-brake technology to be more dangerous than electronic throttle control because it involves removing the physical connection between the driver and the brakes. However, «continuous braking» technology is actually a spectrum of technologies that range from electro-hydraulic to electro-mechanical systems, both of which can be designed to be fault tolerant.
Traditional hydraulic brakes use a master cylinder as well as several slave cylinders. When the driver depresses the brake pedal, he applies physical pressure to the master cylinder. In most cases, this pressure is amplified by a vacuum or hydraulic brake booster. The pressure is then transferred through the brake lines to the brake calipers or wheel cylinders.
Anti-lock braking systems were early forerunners of modern brake-by-wire technologies as they allowed the vehicle to be braked automatically without driver intervention. This is achieved by an electronic actuator that activates the existing hydraulic brakes. A number of other security technologies have also been built on this foundation. Electronic system stable control provisions, traction control and automatic brake the system is all dependent on ABS and peripheral, brake-by-wire technology.
In vehicles using electro-hydraulic wire-braking technology, the calipers located in each wheel are still hydraulically actuated. However, they are not directly connected to the master cylinder, which is activated by pressing the brake pedal. Instead, pressing the brake pedal activates a series of sensors. The control unit then determines how much braking force is required for each wheel and activates the hydraulic calipers if necessary.
In electromechanical braking systems, there is no hydraulic component at all. These true brake-by-wire systems still use sensors to determine the required braking force, but that force is not transmitted through hydraulics. Instead, electromechanical actuators are used to activate the brakes located in each wheel.
Most vehicles use a rack and pinion or worm gear that is physically connected to the steering wheel. When the steering wheel is turned, the rack or steering box also turns. The rack and pinion unit can then apply torque to the ball joints through the tie rods, and the steering box typically moves the tie rod through the shooter arm.
In vehicles equipped with drive-by-wire technology, there is no physical connection between the steering wheel and the tires. In fact, steering wheel systems don’t technically need to use steering wheels at all. When a steering wheel is used, a steering feel emulator is typically used to provide feedback to the driver.
Which vehicles are already equipped with Drive-By-Wire technology?
Tesla has cars that are very close to being fully wired, and they are clearly pushing the envelope with all their might to get approved for autonomous use.
There are no fully mass-produced electric powered vehicles, but a number of manufacturers have created concept vehicles that fit the description. In 2003, General Motors demonstrated an electric drive system with the Hy-Wire concept, and the Mazda Ryuga concept also featured this technology in 2007. Electric drive can be found in equipment such as tractors and forklifts, but even in cars and trucks. this electronic power steering feature still has physical steering.
Electronic throttle control is much more common, with various makes and models using this technology. Brake wire can also be found in production models. Toyota’s electronically controlled brake and Mercedes Benz’s Sensotronic are two examples of this technology.